Merge Two Sorted Lists

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        ListNode * ret;
        ListNode * head, *n;
        if( !l1 && !l2 )
            return NULL;
        if( !l1 )
            return l2;
        if( !l2 )
            return l1;
        if( l1->val < l2->val )
        { 
            head = l1;
            l1 = l1->next;
        }
        else
        {
            head = l2;
            l2 = l2->next;
        }
        ret = head;
        while( l1 && l2 )
        {
            if( l1->val < l2->val )
            {
                ret->next = l1;
                l1 = l1->next;
            }
            else
            {
                ret->next = l2;
                l2 = l2->next;
            }
            ret = ret->next;
        }
        if( l1 )
        {
             ret->next = l1;
        }
        if( l2 )
        {
            ret->next = l2;
        }
        return head;
    }
};